Musical instruments that generate electrical signals, such as the electric guitar, are connected to amplifiers and sound systems using electrical cables. Often the distance between the guitar and the amplifier is significant. The electrical cables have capacitance that increases with cable length. The capacitance in the cable can cause a phase distortion or shift in the electrical signals generated from the musical instrument. The phase distortion can increase with the cable length and create a “muddy” sound. Sometimes an effects pedal (or a “Stomp Box”) is used to modify the instrument's sound. The pedal is usually coupled between the musical instrument and the amplifier. Using the pedal may also adversely affect the sound of a musical instrument through the phenomena called “tone sucking.”
Electric guitars and other stringed instruments can generate electrical signals using pickups. A pickup device acts as a transducer that captures mechanical vibrations (usually from suitably equipped stringed instruments such as the electric guitar, electric bass guitar or electric violin) and converts them to an electrical signal, which can be amplified and recorded. Pickup can be magnetic, piezoelectric, hexaphonic (divided or polyphonic), electromagnetic, or optical. A magnetic pickup consists of a permanent magnet wrapped with a coil of a few thousand turns of fine enameled copper wire. Pickups can be either active or passive. Pickups, apart from optical types, are inherently passive transducers. Active pickups can incorporate electronic circuitry to modify the signal. Active pickups can require an electrical source of energy to operate and include an electronic preamp, active filters, active equalization (EQ) and other sound-shaping features. Typically, 10% of pickups used are active. Passive pickups are usually wire wound around a magnet. Passive pickups can generate electric potential without need for external power, but their output is relatively low.
The frequency range for audible sound is about 20 Hz to 20 kHz for most individuals. This is referred to as the audible range. Pickups can generate a high frequency voltage sine wave in response to high frequency acoustic signals (i.e. sound) in the upper audible range (15-20 KHz) with an amplitude of approximately 60 to 100 mV peak-to-peak. The maximum voltage of a signal produced by a pickup in response to a high frequency acoustic signal may be 300 mV. Pickups can generate a low frequency voltage sine wave in response to an acoustic signal in the lower audible range (2-4 KHz) with an amplitude of approximately 1 V peak-to-peak. Pickups can generate greater voltage for low frequency acoustics than higher frequency acoustics.
Numerous pickups are available to musicians to vary the quality of the sound of their guitars. Different styles of music use different types of pickups. Pickups can be mounted on a musical instrument and are connected to sound equipment using cables. Cables have resistance, capacitance, and inductance, together referred to as the impedance, which can alter the characteristics of the electrical signal, and thus the sound amplified. Using an amplifier to buffer or amplify the generated signal may reduce the effects due to the impedance of the cable and other components, such as an effects pedal.